Phase Transition Engineering for Exciton Dynamics in Atomically Thin Semiconductors

Abstract

Two-dimensional excitonic devices are of great potential to overcome the dilemma of response time and integration in current electronic and/or photonic systems, where dynamically controlling the spatiotemporal dynamics of exciton flux is a cornerstone. Although tip-induced strain engineering and surface acoustic waves (SAWs) have been proposed, the complex accessorial configurations severely limit the applications in integrated devices. Here, we systematically investigate phase transition engineering of vanadium dioxide (VO₂) for exciton dynamics in an atomically thin semiconductor. Temperature-dependent photoluminescence (PL) spectra demonstrate that PL reaches a maximum at the phase transition temperature T_c (340 K), due to the increase in free carrier density during the insulator-to-metal transition. The thermal hysteresis loop is first observed from PL spectra due to the latent heat in the phase transition. The increased free carrier density during the VO₂ phase transition can dynamically modulate the exciton diffusion coefficient, where the enhanced charged excitons (trions) near the insulator–metal transition temperature promote the exciton diffusion coefficient. The hexagonal boron nitride (hBN) intercalation mitigates the VO₂-induced negative effects through dielectric screening and interfacial defect reduction while preserving the dynamic phase transition modulation capability in the PL spectra and yielding a more than doubled enhancement of the exciton diffusion coefficient. These findings highlight the importance of phase transition engineering for two-dimensional (2D) exciton-based devices and lay a foundation for the development of functional excitonic devices.